Water turbines

ABSTRACT

An axial flow water turbine comprises a runner disposed for rotation in a water flow tube and carrying a peripheral drive member such as an electrical generator rotor. The runner is mounted on a stub shaft carried by an upstream supporting structure. The stub shaft is provided with discrete resiliently mounted bearing pads between which and the runner hydrostatic lubrication can be provided. Preferably the stub shaft is hollow and each bearing pad is disposed in a recess formed in the stub shaft, the recess being provided with a detachable backing plate. Thus each pad can be withdrawn radially inwardly into the stub shaft and can be inspected or replaced without necessitating removal of the runner from the stub shaft.

Braikevitch et al. 1 Feb. 22, 1972 [541 WATER TURBINES 3,353,028 11/1967Braikevitch et a1... 290/52 3 422 275 1/1969 Braikevitch et a1 ..290/52[72] Inventors: Michael Braikevitch; Emil Goldwag, both of NethemmEngland 3,466,952 9/ 1969 Greenbreg et a1. ..308/9 Assigneel The EnglishElectric p y Limited, Primary Examiner-Henry F, Raduazo LondongAttorney-Misegades & Douglas, Keith Misegades and 221 Filed: July 17,1970 Gemge DWEMSIJ" [21] App1.No.: 55,641 [57] ABSTRACT Related US.Application Data An axial flow water turbine comprises a runner disposedfor [63] continuatiommpan of Ser No 804 446 Mar 5 rotation in a waterflow tube and carrying a peripheral drive 1969 abandoned member such asan electrical generator rotor. The runner is mounted on a stub shaftcarried by an upstream supporting 52 us. Cl ..415/173 290/52 308/9smmure- The Stub Shaft is Pmvided with (was resiliemly 1 mounted bearingpads between which and the runner hydro- 51 1111. C1. ..F01d 15/10, F160 7/04, Fld /20 mm lubncano" can be Prowded- [58] Field of 1 Preferablythe stub shaft is hollow and each bearing pad is 415/112, 290/52-54,417/356, 310/361, 308/9 disposed in a recess formed in the stub shaft,the recess being provided with a detachable backing plate. Thus each padcan [56] References be withdrawn radially inwardly into the stub Shaftand can be UNITED STATES PATENTS inspected or replaced withoutnecessitating removal of the runner from the stub shaft. 3,080,761 3/1963 Speen ..308/9 3,191,079 6/1965 Gitzendanner ..3 /261 8 Claims, 8Drawing Figures 64 lB 56 Bf 2| 2s Q o 72 x .1 jg 26 24 2| 24 18 i B X m4102 9s 96 94 ll 5 I33 H2 E as 109 loo 109 A/ I10 HO HO f 92 lol 7PATENTEUFEB22 m2 3,644,053

SHEET 1 OF 5 \j J. FIG. I

PAIENIEnnazz 1972 v 3,644,053

SHEET 5 [IF 5 WATER TURBINES This is a Continuation-in-Part ofapplication Ser. No. 804,446, filed Mar. 5, 1969; now abandoned.

This invention relates to axial flow water turbines and pumps of thekind in which a turbine runner is disposed for operation in a water flowtube and arranged for rotation about an axis which is horizontal orsubstantially horizontal. Such turbines and pumps find application in,for example, tidal flow hydroelectric schemes.

In the past the runner of such a turbine has been supported for rotationon a rotatable shaft carried in fixed bearings spaced axially apart, theshaft and runner being secured together for rotation together, and thebearings being carried by supporting structures mounted within the tube,In one simple arrangement the bearings and associated supportingstructures have been mounted on either side of the runner, but thisarrangement has the attendant disadvantage with some types of axial flowturbine that hearing support structures located downstream of the runnerproduce difficult hydraulic flow problems. In particular, with a runnerhaving fixed blades or vanes operating with a variable load and/or froma variable head water supply source, the exit water from the runner hasin general a circumferential motion of magnitude dependent on theoperating load and head, so that for most values of operating load andhead severe and variable circumferential loading is placed on any fixedbearing structure which is located downstream. Furthermore, such adownstream bearing structure produces extra turbulence in the water flowin the draft tube.

Thus for hydraulic flow reasons it is desirable to have the bearingsupporting structures mounted upstream of the runner in the tube, andsuch arrangements have been proposed in the past.

It has also been proposed to mount a generator rotor or other heavyperipheral drive member directly around the runner of an axial flowturbine so as to be carried by the runner and so obviate the need for ashaft to transmit the runner torque to a generator or other load device.

However, since such a generator rotor may, as now envisaged, have adiameter of the order of 20 to 30 feet and a weight of some hundreds oftons, great difficulties arise in supporting the runner and generatorrotor if the shaft and bearing arrangements of the prior art areadopted. Moreover, where a generator rotor is carried directly by therunner the bearing arrangements for supporting the runner must also beable to resist any unbalanced magnetic pull which is exerted on therotor of the generator.

According to the present invention an axial water flow machine includes:

a water flow tube;

a runner disposed within the tube for rotation about a substantiallyhorizontal axis and adapted to carry a peripheral drive member; and

a supporting structure disposed axially to one side of the runner forsupporting the runner within the tube;

wherein the improvement comprises the provision of:

a stub shaft extending from the supporting structure and engaging a boredefined in the runner radially within the said peripheral drive member;and

a plurality of bearing pads carried by the stub shaft to which pads alubricant can be fed under pressure to provide hydrostatic lubricationbetween each pad and the bore, each pad being resiliently mountedradially with respect to the stub shaft.

As compared with the prior art arrangement recited above in which aturbine runner is carried on a rotatable shaft which is itself carriedin two fixed bearings mounted upstream of the runner, the bearingarrangement of a turbine according to the present invention ispositioned relative to the runner so that the load it has to carry, forgiven runner forces, is substantially less than that which the bearingadjacent the runner in the recited prior art arrangement would have tocarry for the same forces acting on the turbine runner.

Furthermore, since the bearing arrangement has been placed at a positionwhere the load it has to support is least, the higher loads to becarried in supporting the stub shaft in a cantilever manner can becarried more satisfactorily in the static support structure that has tobe provided for the boss. This obviates the problem of carrying suchhigher loads on the relatively movable surfaces ofa bearing adjacent butupstream of the runner such as would be encountered in the aboverecitedprior art arrangement.

By obviating the rotating shaft and its two axially spaced fixedbearings of the recited prior art arrangement the bearing clearancespresent in the system have been reduced to those attendant upon the useof a single bearing arrangement, instead of those associated with twobearings, so that the alignment of the runner can be generally moreaccurate and subject to smaller changes under load conditions.

Preferably recesses are formed in the stub shaft and a bearing pad isdisposed in each recess. Each recess may be provided with a backingplate and each bearing pad is located circumferentially and axially bythe recess and is supported radially by a plurality of compressionsprings which bear against the said backing plate.

Preferably also each backing plate is detachable and the stub shaft ishollow such that each bearing pad can be withdrawn radially inwardlyinto the stub shaft.

The bearing pads may be spaced circumferentially around the stub shaft,the circumferential spacing between adjacent pads being greater on theunderside of the shaft than on the upper side. Alternatively oradditionally the bearing pads on the underside of the stub shaft areeach of smaller bearing area than those on the upper side.

There may be two axially spaced circumferentially extending sets ofbearing pads on the stub shaft.

Secured to the stub shaft may be an annular bearing flange which extendssubstantially radially therefrom and cooperates with the runner fortransmitting axial thrust from the runner to the supporting structure,the flange incorporating in its surface a plurality of bearing padsbetween which and the runner hydrostatic lubrication can be provided.

One axial flow 'water turbine and a modification thereof, with aperipheral drive member in the form of a rim-mounted electricalgenerator rotor, according to the present invention, will now bedescribed by way of example and with reference to the accompanyingdrawings, in which:

FIG. 1 shows diagrammatically the general arrangement of the turbine andgenerator, seen from the side with some parts shown in section;

FIG. 2 shows an enlarged view of part of the turbine and generator asseen in FIG. 1, showing in detail the bearing arrangement supporting theturbine runner;

FIG. 3 shows a section taken on the line IIIIII in FIG. 1;

FIG. 4 shows a partly sectioned diagrammatic view of the turbine lookingupstream;

FIG. 5 shows in section the detail ofone fastening device for securingthe generator rotor to the turbine runner;

FIG. 6 shows a section through a modified bearing arrangement forsupporting the turbine runner, transverse to the axis of rotation of therunner;

FIG. 7 shows a perspective view ofone bearing pad as incorporated in thebearing arrangement shown in FIG. 6; and

FIG. 8 shows a half section similar to FIG. 6 but on a larger scale andillustrates another bearing arrangement.

Referring now to FIG. 1, the turbine consists of a runner 2 including ahub assembly 4 with four blades 6. The hub is mounted on a bearingarrangement (shown particularly in FIG. 2) which is carried in anoverhung fashion from a stationary nacelle 8 which is itself carriedcentrally within a water flow tube 9 by four vanes 10. Upstream of therunner there are a number of adjustable control blades 12 which areadjustably pivoted about radial axes, the angle of inclination of allthe blades 12 being varied by rotating a control ring 14 about the axisof the turbine. The ring 14 is pivotally connected to crank arms 16 onthe outer trunnions of the blades 12.

The turbine drives a generator consisting of a peripheral drive memberin the form of a rotor 18 secured directly around the turbine runner,and a stator 20 surrounding the rotor. It will be seen that the rotor 18lies outside the bore of the tube 9 containing the turbine runner, so asnot to obstruct flow through the tube.

A nose cone 22 is secured to the hub assembly 4 to provide streamliningdownstream of the runner.

Two annular seals 12 acting between the rotor 18 and two removabletubular parts 24 disposed on opposite sides of the rotor (and definingpart of the turbine tube) limit the escape of water under pressure fromthe turbine tube between the adjacent parts of the rotor 18 and tubularparts 24. The seals are shown in outline in FIG. 1, and diagrammaticallyin FIG. 2. The detail of the seals will not be described here since thepresent invention is not concerned with them. For details of theconstruction of the seals, the readers attention is directed to theapplicants other application, Ser. No. 804,438 filed Mar. 5, 1969.

The removable tubular parts 24 of the turbine tube have flanges 25 (seeFIG. 2) bolted upstream to an annular part 26 and downstream to anannular part 28 respectively, each such part further defining theturbine tube 9. The end of each tubular part 24 adjacent to thegenerator rotor is formed with an outwardly extending flange 30 whichlies closely adjacent an annular plate 72 secured to the body.

The body portion 32 of the generator rotor is formed with recesses 68for the sake of lightness. Each recess 68 extends circumferentiallyuntil just short ofa runner blade, so that the rotor body portion 32 issolid in the region lying immediately outside each runner blade. Therotor is secured to the runner blades by fasteners '70 (see FIG. 2) ofwhich only one is shown. The cover plates 72 extend over the recesses68. The flanges 30 of the tubular members 24 have recesses which containcircumferentially extending inflatable tubes 74 which can be expanded byinternal fluid pressure to seal against the plates 72 and therebyisolate the seals 21 completely from water in the turbine tube 9. Thisis done when the turbine is stationary and when the seals are to beinspected.

FIG. 5 shows one of the fasteners securing the generator rotor to therunner blades. Each fastener consists of a stud 76 having a threaded endportion 78 which is screwed into the end of the runner blade. The body80 of the stud passes through a clearance hole in the rotor and hasacentral bore into which an electric heating element 82 is insertedduring assembly. Before the current is switched on, a nut 84 istightened on to the outer end of the stud. Heating of the stud by meansof the electric element then expands the stud longitudinally, and whenthe required expansion has been obtained, as indicated for example bythe clearance 86 which then exists between the nut 84 and thecooperating face of the rotor, the nut 84 is again tightened. As aresult, when the stud cools down it is put into tension. Thispretensioning of the studs is desirable in order to prevent thegenerator rotor from expanding through centrifugal force to a point atwhich it parts from the tips of the runner blades. The prestressingshould be such as to prevent such parting during normal running, andpreferably also in'the event of overspeed running, this is to say in anemergency.

This method of securing the generator rotor to the runner is especiallyapplicable to large runners, say of the order of 30 feet in diameter.

Other methods of pretensioning the fasteners may be used. For example,the nut 84 may be tightened to a predetermined extent in order to placethe stud 80 in the desired amount of tension without the use of heating.

There may be, for example, seven or eight studs for each blade, evenlyspaced along the edge ofthe blade.

FIG. 2 shows how the turbine runner is borne by the nacelle 8. Acylindrical stub shaft 88 is secured by bolts 90 to an inwardly directedflange 92 disposed at the downstream end of the nacelle 8, and therunner hub itself surrounds this boss. The hub consists basically of anannular part 94 which has recesses in which root portions 96 of theblades are secured by bolts 98 (of which only one is shown for the sakeof clarity). Within the part 94 thereare two cylindrical liner members100 and 101 whose internal cylindrical surfaces constitute the internalbearing surface of the hub. A further annular part 102 which cooperateswith the upstream end of the hub is secured to the nacelle by bolts 104,and has a water seal formed by a gland 106 engaging between the part 102and a rotary part 108 secured to the annular part 94 of the runner.

It should be noted that this single bearing arrangement for supportingthe runner and the generator rotor lies substantially symmetrical withinthe runner and rotor. In other words, the center of gravity of therunner and rotor lies substantially centrally within the bearingarrangement.

The stub shaft 88 has a cylindrical external bearing surface in whichare formed two axially spaced sets of circumferentially spaced pockets109 into which high-pressure oil is fed via constriction orifices (notshown) to support the runner in the manner of a hydrostatic hearing. Inother words, the oil pressure supplied is sufficient to lift the linermembers slightly from the boss and to maintain a slight runningclearance between them and the boss. Though the pockets 109 arepositioned all the way around the hub, they are more widely spacedaround the bottom part of the hub. Oil escaping axially from the pockets109 is bled away through passageways (not shown) extending from completecircumferential grooves 110 in the liner members, except that oilescaping from the downstream pockets 109 is extracted from acircumferential recess 112. v

This recess 112 isolates the adjacent pockets 109 from pockets 114formed in a thrust bearing flange 117 which is secured to the downstreamend of the stationary boss 88 and which cooperates on the upstream sidethereof with an outwardly extending flange of the downstream linermember 101 and on the downstream inside thereof with a runnerretainingmember 133 which is secured to the annular part 94 of the hub.

As will be seen from FIG. 2 the stationary thrust bearing flange 117 hastwo sets of pockets 114 formed in the opposite surfaces thereof. Thesetwo sets of pockets 114 are supplied with lubricating oil throughseparate constriction devices so that the thrust-bearing arrangementoperates in the manner of a hydrostatic bearing to control the axialposition of the turbine runner.

Though the pockets 109 and 114 have been described and shown as beingformed in the stationary parts of the bearing arrangements, they couldif desired be formed in the associated moving parts.

In a preferred modification of the bearing arrangements described aboveeach of the pockets 109 and 114 has disposed within it a bearing padwhose bearing surface is raised above the level of the surface intowhich the pad is inserted, so that the stationary bearing surfaces areconstituted solely by the bearing surfaces presented by the pads to themoving surfaces of the runner.

Openings formed centrally in each of the pads provide passages enablinglubricating oil supplied to the pockets as described above to issuebetween the stationary and moving bearing surfaces. In the FIGS. 6 and7, the pockets 109 in the stub shaft 88 are occupied by bearing pads 134having central openings 135 which open into the corners of square-shapedgrooves 136.

Since the bearing surfaces of the pads in the pockets 109 carry therunner, the stub shaft 88 need not have a cylindrical shape, but merelya shape suited to supporting the bearing pads in the desired positions.Furthermore, the area of the bearing pad surfaces may be made to suitthe magnitude of the runner load and forces only, and need not be suitedto the size of boss which is necessary to give the runner adequatepositional stability under all conditions of water head and load. Thisprovides the advantage that the bearing frictional losses are kept to aminimum, and are not determined by a bearing shaft size designed to givethe desired positional stability of the runner.

As compared with the bearing arrangement described with reference to theFIG. 2 in which the hub and boss have complementary internal andexternal cylindrical bearing surfaces with oil admitted to the pockets109, the modified arrangement of FIGS. 6 and 7 using pads in the pocketsprovides an arrangement in which the rate of flow of lubricating oilthrough the bearing is lower for the same oil pressure. This economizesin the horsepower required to circulate the hearing oil against thebearing film pressure.

In a preferred form of bearing as illustrated in FIG. 6, the runner hubliners 100, 101 are supported on two axially spaced sets of bearing pads134 carried in pockets 109, and each set comprises three upper padsdistributed symmetrically over the crown of the stub shaft 88 and asingle lower pad, all positioned as shown in FIG. 6.

In each set the three upper pads are designed to carry the runner loadand forces, together with the downward force exerted on the hub by thelower pad, while the lower pad is designed to provide a mechanism forautomatically maintaining the oil film thickness on the three upper padssubstantially constant regardless of runner operating conditions. Tothis end the flow of oil to the upper and lower pads is regulatedautomatically by separate constriction devices 137, 138 connected in theoil supply pipes 139, 140 feeding the upper and lower pads respectively.

Hence in each set of pads a reduction in the thickness of the oil filmon the upper pads due to an increase in runner forces results in a,simultaneous increase in the thickness of oil film on the lower pad, anda consequent increased flow of oil and reduction of oil pressuresupplied to the lower pad. This reduction of oil pressure on the lowerpad reduces the downward force exerted by the lower pad on the runnerhub, so that the downward force exerted by the runner hub on the upperpads decreases, thus allowing the oil film on the upper pads toincrease.

It will be appreciated that in the bearing arrangements described theload carried by the upper bearing pads includes a contribution due tothe downward force exerted on the rotor hub by the lower pads. Hence thepreferred arrangement of FIG. 6 provides an advantageous arrangement, inthat the downward force exerted on the hub by the lower bearing padarray is kept to a low value (there being only one lower pad), andreduces the size of the bearing pads to be provided on the upper side ofthe boss, and of the hoop stresses in the runner hub.

Though in the above description the bearing surfaces have been providedon pads located in the pockets 109 and 114, such bearing surfaces couldbe provided on raised portions of the cylindrical boss 88 and of thethrust-bearing flange 117. However, the use of separate pads representsa much more economical form of construction.

Referring to FIG. 8, in which like parts bear identical references tothose used in the earlier figures, there is shown a preferred form ofbearing in accordance with the invention in which bearing pads 134 arelocated axially and circumferentially in recesses or pockets 109 formedin the surface of a stub shaft 88. The floor of each recess 109 isformed by a backing plate 160 which is bolted to a spot-face machined onthe inner surface of the stub shaft 88. Removal of the bolts (not shown)allows the backing plate 160 and the bearing pad 134 to be withdrawnradially inwardly from the surface of the shaft for maintenance orreplacement. A trolley 162 having flanged wheels 164 which run on rails166 is provided within the shaft for movement of backing plates andbearing pads between the runner and an access point in the supportingstructure 8. 10 (see FIG. 1). By virtue of this arrangement a bearingpad can be replaced without the need to remove the runner from the stubshaft 88.

Each bearing pad 134 is a sliding radial fit between the walls of itsrecess 109.v With the backing plate 160 bolted in place the pad 134 isurged radially outward by four stacks of conical spring washers 168 (ofwhich only two are shown in FIG. 8). Each stack of washers is located bya stud 170 screwed into the backing plate. Lubricating oil is suppliedunder pressure to each bearing pad 134 in a similar manner to thearrangement shown in FIGS. 6 and 7. A flexible portion (not shown) ishowever introduced into each supply pipe 139, 140 (FIG. 6) where itcommunicates with the pad 134 in order to accommodate radial movementexperienced by the pad as a result of its resilient mounting.

The resilient mounting of the bearing pads 134 has application tobearing arrangements of any size, but it will be appreciated that with amachine of such size as has been described above the resilience will beof especial advantage in accommodating small machining inaccuracies aswell as strains caused by the dead weight of the runner and bycentrifugal forces.

It will be seen that in the bearing arrangement shown in FIG. 8 there isa set of four circumferentially spaced bearing pads 134 (only two beingshown since FIG. 8 is a half section), the lower pads being smaller inbearing area than the upper pads. This represents a slightly differentmethod of achieving the effect sought by the arrangement shown in FIG. 6in which the lower pads are reduced in number rather than in bearingarea.

The forms of bearing described above facilitate the overhung mounting ofthe runner. Overhanging of the runner is an advantage because of theomission of downstream support vanes which necessarily give rise tolosses.

It should be noted that the axial extent of the turbine hub assemblyextending from the left-hand end of the stub shaft 88 to the left-handend of the nose cone 22 is less than the distance between the endflanges 25 of the tube portions 24. The arrangement is such that theentire turbine runner and generator rotor, together with the tubeportions 24, can be withdrawn vertically or laterally for servicing,after first removing the end cone 22, disconnecting the stub shaft 88and annular part 102 from the nacelle (by withdrawing the bolts and104), and disconnecting the flanges 25 of the tube portions 24 fromtheir cooperating attachment points. The flanges 25 may for example bebolted to corresponding flanges on further tubular parts forming linerswithin the concrete surrounds 116 and 118. This arrangement enables therunner and generator rotor and also the generator stator to be readilyserviced; while this servicing is being carried out a replacement setmay be inserted so that the turbine set can continue to operate.

It should be noted, as shown in FIG. 3, that the vanes 10 carrying thenacelle 8 are set at 45 to the horizontal. This enables their outer endsto be anchored close to the ends of two horizontal beams 120 and 122lying respectively above and below the water tube, which beams areconnected to four sole plates 124 built into concrete walls extendingaxially from upstream to downstream of the runner, past the generatorstator 20, to the foundations surrounding the turbine tube downstream ofthe runner. This arrangement is particularly useful where there is adesire not to have the thrust on the runner felt as a pull on the damconstruction upstream of the runner.

One of the vanes identified as 10A in FIG. 3 is hollow and has astreamline cross section (apparent from FIG. 1), to provide an access topoint to the nacelle and hub whereby to enable inspection of the variousparts to be carried out.

Electrical leads for connection to the generator rotor pass through thehollow vane 10A and along a path indicated approximately by thechain-dotted line 126 (see especially FIG. 1), a slipring assembly 128being provided in the nose cone to enable electrical connection betweena stationary supply cable 130 (shown in FIG. 2) and a cable 132 disposedin one of the runner blades 6 for supplying the generator rotorwindings.

The lower bearing pad shown in FIG. 6 may be omitted in some instancesprovided that rubbing rings are fitted around the lower part of the stubshaft to prevent damage of the internal bearing surface of the runnerhub in the unexpected event that the runner is subjected to a suddenhigh side thrust. The lower bearing pad shown in FIG. 6 provides anautomatic stabilizing action to maintain the runner rotating about itsdesired axis when such side thrusts occur, and so prevent damage of therunner bearing surface.

We claim:

1. An axial water flow machine including:

a water flow tube;

a runner disposed within the tube for rotation about a substantiallyhorizontal axis and adapted to carry a peripheral drive member;

a supporting structure disposed axially to one side of the runner forsupporting the runner within the tube;

wherein the improvement comprises the provision of:

a stub shaft extending from the supporting structure and engaging a boredefined in the runner radially within the said peripheral drive member;

a plurality of bearing pads carried'by the stub shaft, means whereby alubricant can be fed under pressure to provide hydrostatic lubricationbetween each pad and the bore, and means whereby each pad is resilientlymounted radially with respect to the stub shaft.

2. A machine according to claim 1, wherein recesses are formed in thestub shaft and a bearing pad is disposed in each recess.

3. A machine according to claim 2, wherein each recess is provided witha backing plate and each bearing pad is located circumferentially andaxially by the recess and is supported radially by a plurality ofcompression springs which bear against the said backing plate.

4. A machine according to claim 3, wherein each backing plate isdetachable and the stub shaft is hollow such that each bearing pad canbe withdrawn radially inwardly into the stub shaft.

5. A machine according to claim 1, wherein the bearing pads are spacedcircumferentially around the stub shaft the circumferential spacingbetween adjacent pads being greater on the underside of the shaft thanon the upper side.

6. A machine according to claim 1, wherein the bearing pads on theunderside of the stub shaft are each of smaller bearing area than thoseon the upper side.

7. A machine according to claim 1, wherein there are two axially spaced,circumferentially extending sets of bearing pads on the stub shaft.

8. A machine according to claim 1, wherein secured to the stub shaft isan annular bearing flange which extends substantially radially therefromand cooperates with the runner for transmitting axial thrust from therunner to the supporting structure, the flange incorporating in itssurface a plurality of bearing pads between which and the runnerhydrostatic lubrication can be provided.

1. An axial water flow machine including: a water flow tube; a runnerdisposed within the tube for rotation about a substantially horizontalaxis and adapted to carry a peripheral drive member; a supportingstructure disposed axially to one side of the runner for supporting therunner within the tube; wherein the improvement comprises the provisionof: a stub shaft extending from the supporting structure and engaging abore defined in the runner radially within the said peripheral drivemember; a plurality of bearing pads carried by the stub shaft, meanswhereby a lubricant can be fed under pressure to provide hydrostaticlubrication between each pad and the bore, and means whereby each pad isresiliently mounted radially with respect to the stub shaft.
 2. Amachine according to claim 1, wherein recesses are formed in the stubshaft and a bearing pad is disposed in each recess.
 3. A machineaccording to claim 2, wherein each recess is provided with a backingplate and each bearing pad is located circumferentially and axially bythe recess and is supported radially by a plurality of compressionsprings which bear against the said backing plate.
 4. A machineaccording to claim 3, wherein each backing plate is detachable and thestub shaft is hollow such that each bearing pad can be withdrawnradially inwardly into the stub shaft.
 5. A machine according to claim1, wherein the bearing pads are spaced circumferentially around the stubshaft the circumferential spacing between adjacent pads being greater onthe underside of the shaft than on the upper side.
 6. A machineaccording to claim 1, wherein the bearing pads on the underside of thestub shaft are each of smaller bearing area than those on the upperside.
 7. A machine according to claim 1, wherein there are two axiallyspaced, circumferentially extending sets of bearing pads on the stubshaft.
 8. A machine according to claim 1, wherein secured to the stubshaft is an annular bearing flange which extends substantially radiallytherefrom and cooperates with the runner for transmitting axial thrustfrom the runner to the supporting structure, the flange incorporating inits surface a plurality of bearing pads between which and the runnerhydrostatic lubrication can be provided.